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PWM controller simplifies flyback converter design

Posted: 30 Apr 2007     Print Version  Bookmark and Share

Keywords:DC/DC controller  flyback converter  PWM controller 

Linear Technology Corp. introduced a current-mode PWM controller that reduces the size and complexity of flyback, boost and SEPIC power supplies. The LTC3873 is suitable to design high-efficiency, single-ended isolated and non-isolated flyback converters rated up to 25W for telecommunications, networking equipment, PoE, automotive, consumer and general-housekeeping power supplies.

The LTC3873 is suitable for wide input voltage range applications where the input can vary from 9V to 75V during start-up. It is able to sustain operation from 4V to 75V after start-up, enabling users to have one power supply for 48-, 24- and 12V nominal input systems.

The LTC3873-5 is a product version with a 3.9V under-voltage lockout, which allows converters to operate and start from a 5V input source up to 75V. This makes the part suitable for boost conversion from a 5V input source to 12-, 24-, 48V and higher output voltages.

A current sense resistor is optional and the current limit threshold is programmable, allowing the use of a wide variety of external MOSFETs for different topologies. The LTC3873/-5 can regulate output voltages as low as 0.8V and has an integrated soft-start function that limits inrush current, reducing output voltage overshoot. The operating frequency is fixed at 200kHz and constant frequency operation is maintained down to light loads, resulting in less low frequency noise generation over a wide range of load currents. With its ultra-low 50µA start-up current, the IC allows the use of a high-value input resistor and a low-value capacitor for low power dissipation and quick power supply start-up. With a standby quiescent current of only 300µA, the LTC3873 is an excellent choice for automotive applications.

The LTC3873 is offered in an 8-lead 2-by-3mm DFN and 8-lead TSOT-23 packages and has an operating temperature range from -40°C to 85°C. The 1,000-piece price starts at Rs.55 ($1.25).

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